1. Field of the Invention
The invention relates to plates made of glass material, more particularly designed to equip ranges, such as tempered glass plates or glass-ceramic plates. Such plates made of tempered glass are used more particularly to form the tops of gas ranges, the burners being able to pass through said tempered glass plates. Glass-ceramic plates am designed more particularly to cover heating elements.
While not limited to such applications, the invention will be described more specifically in reference to glass-ceramic plates that make up the top portion of ranges. These types of ranges comprise heating elements such as radiant or halogen heating units and control mechanisms to vary their intensities.
2. Description of the Related Art
These various elements are placed in a structure, usually a metal structure, and covered with a glass-ceramic plate, which closes the structure. Assembly of these cooking surfaces is therefore completed by placing the glass-ceramic plate onto the metal structure. This manufacturing step is accomplished by adhesive bonding using a silicone adhesive, which is suited to this type of use. Indeed, the silicone adhesive performs various types of functions. First of all, it makes it possible to keep the glass-ceramic plate on the structure in a specific position; a range manufactured in this way can be transported easily, since all the elements are attached to one another. Another function of the silicone adhesive is to ensure that the enclosure formed by the metal structure and the glass-ceramic plate remains leak-proof. This enclosure must first have good tightness so that in the event something boils over, water does not get inside and risk causing a short-circuit. Secondly, from a hygienic standpoint, since this type of plate is a tool for preparing food, it is necessary to prevent areas that are difficult to access and impossible to clean from getting dirty in order to avoid germ growth.
Another function of the silicone adhesive is to absorb mechanical impacts: on the one hand, it prevents any direct contact between the metal structure and the glass-ceramic plate, and, on the other hand, it can compensate for the thermal expansion of the metal structure since the glass-ceramic plate has virtually no expansion coefficient. One feature of silicone adhesives is that they have good temperature resistance. Although the silicone adhesive is only used on the periphery of the glass-ceramic plate and therefore at some distance from the heating areas, this temperature resistance is important: first of all the periphery of the glass-ceramic plate nevertheless experiences a rise in temperature when one or more heating units are in operation. Furthermore, a heated item such as a saucepan can be placed on the edge of the plate and thus quickly subject the adhesive to a high temperature.
A final function of the silicone adhesive for certain assemblies is aesthetic in nature: since at least some of the adhesive is applied on top, it is important to be able to smooth it in order to give it an attractive appearance, for at least some will remain visible; silicone adhesive is easy to shape.
On the other hand, this assembly process, which consists in gluing the glass-ceramic plate onto the metal structure using a silicone adhesive, has various disadvantages. First of all, it requires a relatively large quantity of silicone adhesive; the high cost of this product is a first disadvantage. Indeed, it appears that during assembly the quantity of silicone necessary to fill the entire space between the plate and the frame is large; additionally, some of the silicone used is useless or removed. The silicone can be useless when it unintentionally overflows the adhesive area and is removed, particularly during smoothing. Another disadvantage is linked to the polymerization time, which increases with the quantity of material and which also leads to an increase in manufacturing costs, particularly due to the necessity of providing intermediate storage for the plates.
Additionally, another disadvantage particularly linked to this long polymerization time involves the assembly itself The glass-ceramic plates are usually delivered as-is to the range manufacturers who are responsible for the assembly. In theory, this type of factory assembly, where the workers have the necessary tools, does not present any problems. On the other hand, this type of assembly seems much more difficult for a tradesman who must remount a glass-ceramic plate onto a metal structure after making electrical repairs or in order to replace a glass-ceramic plate that has been damaged. It seems to be a difficult task for the tradesman to attach the glass-ceramic plate, for he must place the silicone adhesive on the periphery of said plate, on the internal surface and on the edges, smooth the adhesive in any visible areas, and keep the glass-ceramic plate well-centered while applying pressure during all these operations and during the polymerization time for the adhesive, which is relatively long.
Furthermore, removing this type of glass-ceramic plate previously attached to a metal structure using silicone adhesive is not easy either, particularly for a tradesman. The tradesman must make a cut in the silicone adhesive underneath, i.e., on the internal face of the glass-ceramic plate, and a cut on top, i.e., on the edge of said plate. These two operations, which must be done along the entire periphery, are not simple, for the two cutting lines must meet in order to separate the two elementsxe2x80x94glass-ceramic plate and metal structurexe2x80x94successfully. Furthermore, and more particularly when cutting on the internal face of the glass-ceramic plate, it is not easy to make this cut without scratching the internal face of the plate. A scratch can lead to a crack during stress and therefore to a break in the plate. It therefore appears virtually impossible to remove a glass-ceramic plate in order to reinstall it later without damaging the plate. Furthermore, in order to reattach it to the structure, it is necessary to eliminate the traces of silicone adhesive from the previous assembly to the greatest extent possible, which also creates a risk of scratching, particularly on the bottom face of the glass-ceramic plate, thereby making this plate more fragile.
As a consequence, in order to replace or remove a glass-ceramic plate it is now customary to work on the entire plate-metal structure unit, that is, it is first necessary to remove the range top, which is usually built into a cooking surface, then to remove the plate connected to a part of the metal structure from the rest of the metal structure. In no case is it possible at present to consider completely separating the plate from the metal structure onto which it is glued.
The aim of the invention is to eliminate these disadvantages and more specifically to propose a plate made of glass material such as tempered glass or glass-ceramic for which mounting onto a metal or equivalent structure is less costly than the techniques cited previously, particularly with regard to the adhesive material, and which can be removed and replaced, if necessary, simply and without any danger of damaging the glass-ceramic plate.
The invention also targets this type of plate made of glass material whose the mounting means will ensure tightness, mechanical impact absorption and temperature resistance, and will give the unit an attractive appearance.
These goals are achieved in accordance with the invention by a plate made of glass material such as tempered glass or glass-ceramic designed to be mounted in a frame, a metal frame, for example, comprising at least one polymer strip on its periphery, said strip having on at least one portion of its length a shape that allows the plate to nest with the frame and thereby be fixed inside it.
By periphery is meant the peripheral area of the plate of glass material; that is, the strip can cover at least part of the edge of the plate and/or at least a peripheral part of one surface of said plate.
In accordance with the invention, mounting is achieved by a strip with a section sized so that it has the necessary and sufficient quantity of material to perform its function Furthermore, since mounting is accomplished by nesting, it is simple to do and can be reversed. Preferably, nesting is accomplished by choosing a polymer strip that can be elastically deformed.
One mode of embodiment of the invention provides that the shape present on the strip is hollow and that it joins with a complementary raised section provided in the frame.
According to another preferred mode of embodiment of the invention, the shape on the strip protrudes, and it fits into a complementary elongated slot or hollow shape in the frame. According to either of these modes of embodiment, the plate of glass material is mounted in the frame simply by mechanical pressing. Effectively, the elastic deformation of the strip and therefore of the protrusion, if such exists, makes it possible by pressing to insert the plate into the frame by deforming the strip, which returns to its initial shape once the protrusion reaches the housing designed for this purpose in the frame. Advantageously, the dimensions and the shape of the strip are such that once the plate is inserted into the frame, this frame exerts pressure on the strip on the periphery of the plate. This type of joining therefore makes it possible to ensure good tightness between the plate of glass material itself and the frame.
To accomplish this, in accordance with a variation of the invention, the polymer strip is, for example, placed along the entire edge of the plate and optionally on a portion of the lower face, so that the strip performs both the mounting and tightness functions.
In accordance with other variations of the invention, the plate comprises at least two strips, one covering all or part of the edge of the plate and ensuring tightness, the other covering another part of the edge and/or a portion of the lower face of the plate and making it possible to mount the plate.
These embodiment variations separate the mounting and tightness functions, each being performed by a different strip. These types of embodiments can make it possible to limit further the quantity of material needed to produce these strips. Furthermore, they can make it possible to produce strips using different materials, with basically different shapes, for example one might be continuous, the other discontinuous, or even to produce strips using different techniques.
In accordance with a preferred mode of embodiment of the invention, the strip comprises the shape over its entire length, and this shape fits into a complementary shape provided along the entire periphery of the frame. This type of embodiment provides a particularly secure mounting. However, the dimensions of the shape are advantageously designed for easy removal of the plate. For example, this can be done using suction cups positioned on at least one corner of the plate.
The material making up the strip must be a material with sufficient temperature resistance, i.e., stable to approximately 200xc2x0 C. Advantageously, after polymerization, the material has elastic properties. It is also preferably inert with respect to foods and stable with regard to detergents or other cleaning materials that might be used in a kitchen in particular.
In accordance with an advantageous variation of the invention, the strip is a silicone such as those marketed by RHONE POULENC under the names RTV 585, RTV 1525, or one of the silicones marketed by WACKER under the name ELASTOSIL LR 3004/50.
In accordance with other variations, the strip may be produced using fluorinated elastomers like the one marketed by the SAFIC-ALCAN Corporation under the name VITON or the one marketed by the 3 M Corporation under the name FLUOREL. While these materials meet the use requirements, they are less attractive from a financial standpoint.
The invention therefore makes it possible, primarily compared to known techniques, to limit the quantity of silicone used, the strip being fully produced prior to mounting and therefore with the necessary and adequate dimensions.
Additionally, there are numerous techniques for using these materials to produce a strip.
In accordance with an initial variant of the invention, the strip is produced by duplicate molding and more specifically by injection molding. Particularly in the case of a strip made of silicone, there are various techniques for producing said strip, particularly depending on the choice of silicone. These techniques most often consist in hot-curing the silicone to transform it within a short period from a paste-like state to a solid state that is relatively elastic. A first method more particularly suited to silicones with high viscosity consists of very high pressure injection of the EPDM (ethylene-propylene-diene) type. This technique consists in injecting silicone into a mold kept at 200xc2x0 C. with very high pressures. This technique requires many precautions in order to prevent the plates of glass material from breaking due to the high pressures.
Another technique suited to bi-component paste-like silicones whose viscosity is between 200,000 and 2,000,000 mPa.s is high pressure thermoplastic injection into a mold heated to 200xc2x0 C. The pressures used are thus less dangerous for the plates of glass material.
A final technique more suited to silicones whose viscosity is closer to liquids is low pressure high frequency injection. Unlike the previous techniques, the mold is refrigerated, and the material is heated under the influence of the high frequency electrical field. In the case of silicones, additives such as FREQUON additives are added to improve the sensitivity of the high frequency field. This last technique has the advantage of being very fast.
According to another variant of the invention, the polymer is produced by extrusion in situ. This type of technique is described, for example, in patent EP 0 524 092 for other applications involving automobiles. This technique can be used more particularly with silicones.
According to a final variant of the invention, the strip is extruded beforehand and attached to the plate of glass material by clipping or gluing. This last variant offers advantages for recycling of the materials: separating the strip and the plate appears to be very simple, particularly in tie case of clipping.
The various methods described for producing the strip in accordance with the invention allow one to obtain a strip with the desired shape that can perform the mounting and tightness functions without any surplus of material.
It is therefore possible to prepare plates of glass material, such as glass-ceramic plates combined with a strip, ready to be mounted into a frame.
The subsequent assembly step can therefore be simplified as compared to the previous techniques, and can be very fast, since no wait time is necessary.